if it all it needs is for the nand to be flashed, they probably do that at gp2xstore. i don't know that for sure though.
most of the gp2x hardware repairs that are done seem to be done personally by craigix (uk) and evildragon (germany). check with gp2xstore first, but you may have to ship it farther.
the d-pad mods are pretty much over with, unless someone comes up with a new design with easier to source parts. but i have a feeling that dave used the best parts for the job, and that his design is solid. if someone comes up with a new design, it may not be as good.
but anyway, for the time being there's unfortunately no simple way to get that mod done. all sold out, you could say.